One of the favorite arguments of climate-change deniers is “but it was warmer in the late 90s.” In fact, the odds are good that I’ll get that argument from George Will on This Weak tomorrow. I basically know the answer: temperature is a noisy time series, so if you pick and choose your dates over a short time span you can usually make whatever case you want. That’s why you need to look at longer trends and do some statistical analysis. But I thought that it would be a good thing to look at the data myself.

So what are the two things you notice right away? Well, one is “cycles”. In fact, if you go back even further you’ll see the same sorts of cycles repeated through out our planet’s history. Looking at data from 1850 in the context of climate change history is to use an eyeblink of data for comparison (coming out of the depths of a centuries long planetary cold spell). It is a classic misuse of limited data in an attempt to support a point of view. It certainly can’t be called “science”.

And secondly, our temperature now isn’t much different than in the 1000’s (not to mention there is much debate as to whether the temperature measurements of today are even accurate), with a very small population relative to today and with no industry, no burning of fossil fuel, and no worries about “green house gasses”. How in the world can that be?

Water vapour was responsible for 95 per cent of the greenhouse effect, an effect which was vital to keep the world warm, he explained.

“If we didn’t have the greenhouse effect the planet would be at minus 18 deg C but because we do have the greenhouse effect it is plus 15 deg C, all the time.”

The other greenhouse gases: carbon dioxide, methane, nitrogen dioxide, and various others including CFCs, contributed only five per cent of the effect, carbon dioxide being by far the greatest contributor at 3.6 per cent.

However, carbon dioxide as a result of man’s activities was only 3.2 per cent of that, hence only 0.12 per cent of the greenhouse gases in total. Human-related methane, nitrogen dioxide and CFCs etc made similarly minuscule contributions to the effect: 0.066, 0.047, and 0.046 per cent respectively.

“That ought to be the end of the argument, there and then,” he said.

“We couldn’t do it (change the climate) even if we wanted to because water vapour dominates.”

Yet the Greens continued to use phrases such as “The planet is groaning under the weight of CO2” and Government policies were about to hit industries such as farming, he warned.

“The Greens are really going to go after you because you put out 49 per cent of the countries’ emissions. Does anybody ask 49 per cent of what? Does anybody know how small that number is?

“It’s become a witch-hunt; a Salem witch-hunt,” he said.

And Krugman seems to be trying out for head inquisitor. There are the numbers Mr. Krugman. Why not try crunching those instead of selectively picking the data that supports your point of view. You wouldn’t stand for that in the economic world. Why should we put up with it from you when you talk about science?

And as I watched the deniers make their arguments, I couldn’t help thinking that I was watching a form of treason — treason against the planet.

Quite an argument, isn’t it – “disagree with me and the “consensus” and you’re committing “treason against the planet?”

You have to wonder, would disagreeing over economic policy be “treason against the economy” in Krugman’s wacky world? How desperate are you when you have to resort to name calling like “traitor” over a policy dispute?

UPDATE II: Irony alert Ezra Klein referring to the Krugman chart above which begins at the end of the period known as the “Little Ice Age”:

Paul Krugman has a nice response to the variant of global warming denialism favored by the statistically illiterate.